hard lead vs Pb

hard lead and Pb both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard lead	Yes	No	No	No
Pb	Yes	No	No	No

As nouns, Pb is a hypernym of hard lead; that is, Pb is a word with a broader meaning than hard lead:

hard lead: a lead alloy that contains about 5% antimony
Pb: a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey

Other hypernyms of hard lead include atomic number 82, lead.

As nouns, Pb is a hypernym of hard lead; that is, Pb is a word with a broader meaning than hard lead:

hard lead: unrefined lead that is hard because of the impurities it contains
Pb: a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey

Other hypernyms of hard lead include atomic number 82, lead.

hard lead (noun)	Pb (noun)
a lead alloy that contains about 5% antimony	a unit of information equal to 1000 terabits or 10^15 bits
unrefined lead that is hard because of the impurities it contains	a soft heavy toxic malleable metallic element; bluish white when freshly cut but tarnishes readily to dull grey